Here's a way to get textures for certain blocks and/or mobs that cant be generated yet using the new PPC generators!

Go to https://mcasset.cloud/ This is a new website I found that has every single Minecraft version's textures for you to download! Once you select a version using the drop-down, scroll down and click ".zip" next to "Download." If you log in using GitHub, however, you can browse through the files and download texture images directly, without the need to go through that .zip. Texture files will be found under assets/minecraft/textures, then either under "entity" or "block." Once you find something you want to download, you can right-click and select "save image as" to save it directly as a .png file.

If you downloaded using the .zip option, in your downloads folder(or wherever you downloaded the resource pack) extract the resource pack's .zip Now, you can navigate through the folder and go through it just as if you were doing it in the website as I explained above.

If you just want the block generator to use 1.14 textures, check out https://generators.pixelpapercraft.com/ for the new and HEAVILY improved block generator.

If you have any questions/problems, then ask me on discord! M16#4150

Hope this helped! :D